• Testing new PCB revision

    Steven Merrifield06/20/2020 at 03:23 0 comments

    I've completed a new layout and built a prototype which works well.

    Updates include:

    - removal of the Holt IC, now replaced with a custom analog front end using a high speed comparator

    - changed CH340G to CH340E (smaller, and doesn't require a 12MHz clock from the FPGA)

    - changed USB mini to USB micro

    - changed 3.3V/1.2V linear regulator to a larger package to simplify soldering - the previous package was just too small

    - changed a few 0805 packages to 0603

    - new PCB fabricator (JLCPCB) since they can do stencils as well as supply most of the parts

  • Custom 429 comparator

    Steven Merrifield03/21/2020 at 02:37 0 comments

    My ARINC 429 to USB receiver has been using a proprietary front end chip made by Holt IC. This is expensive and locks me into a single-source supplier (it's the most expensive part on the board, even more expensive than the FPGA!). I've been working on removing the Holt receiver and replacing it with a discrete front end. I have now completed a design and successfully tested it. Although it uses slightly more board space, my discrete design is much cheaper and even out performs the Holt chip in terms of it's ability to handle DC offsets so I am very happy. 

    Here is an example of my discrete front end receiving low speed (12.5k) ARINC 429:

    And here is an example of my discrete front end receiving high speed (100k) ARINC 429:

  • Conversion to single-sided

    Steven Merrifield03/21/2020 at 02:20 0 comments

    Lately I've been working on converting the original double-sided board into single-sided. This project is starting to become popular on Tindie and I'm selling quite a few, so reducing the manufacturing time has become important. Moving from double-sided to single-sided has increased the size of the board slightly, but it's still small enough to fit two on a 50x50 panel. As of Feb 2020, all new orders will receive the single-sided version.